A new in vivo method to investigate antibiotic penetration and concentration in spontaneous infectious spondylodiscitis.

Spontaneous discitis is unusual and typically affects children. Hematogenous delivery of an infectious organism is the likely main cause. Common treatment method including conservative and surgical treatments, which also needs prolonged antimicrobial therapy based on an effective inhibitory concentration, can be achieved on the local disc space. Intradiscal antibiotic concentration was measured after the disc was harvested after preventive administration of antibiotics in previous studies. On the one hand the disc cannot simulate the infection situation when the inflammation leads to end plate destruction, vascular invasion and increase of permeability. On the other hand antibiotic concentrations were measured in vitro which cannot tell the actual situation in vivo. It is necessary to find a reliable evaluation method to decide whether the antibiotic can penetrate and make an effective inhibitory concentration in the local disc at the beginning of the treatment in vivo. Systemic antibiotics like nutrients enter and leave the disc by the only way of passive diffusion. The postcontrast MRI has been widely used as a noninvasive method of studying transport into the disc. The enhancement following contrast administration can be measured in T1 sagittal MR images by placing suitable cursors and evaluating the signal intensity (SI) of the region. Therefore we hypothesise that serial postcontrast MRI can be used to measure antibiotic concentration in the infected intervertebral disc in vivo. If the hypothesis is verified, we can better determine the choice of antibiotics and antibiotic treatment regime at the beginning of the treatment to improve the treatment success rate.